FR2630920A1 - TENNIS RACKET - Google Patents

Abstract

A tennis racket of oval overall shape is characterized in that the face comprises five regions. The geometric centre (M), the hilting centre (P) and three transverse strings are located in a central region (A), and three transverse strings the mean length of which is greater than that of the region (A) are located in each of two regions (B and C). The area in which the elasticity is substantially unifrom is thereby increased.

Description

TENNIS RACKET
The present invention relates to a racket for tennis constituted by a frame delimiting a corded surface, a handle joined to the frame by a part comprising a void between the ends of the frame then meeting to form the handle, a spacer closing the frame, the end opposite to the handle is generally called head, the corded surface being formed of strings generally called uprights, parallel to the axis of symmetry X of the frame lying in the extension of the handle, and of strings generally called through, parallel to a axis Y perpendicular to the X axis and passing near the middle of the X axis.

By 1965, the size of the corded surface of most tennis rackets had remained unchanged for many years, and rarely exceeded 451 cm2. But, from 1970, the use of metal and especially plastics reinforced with glass fibers, then carbon, boron or ceramic, made it possible to manufacture so-called "large sieve or large basket" frames, including the cordate surface can reach 680 cm2, that is to say more than 50% increase compared to the usual conventional surface of 451 cm2, whose more or less oval shape has a length sometimes exceeding 34 cm and a width may exceed 26 cm. Such rackets are described in US-A-3,999,756.

With such corded surfaces, the lengths of the uprights and beams are naturally increased. This results in a better elasticity of the entire rope and a widening of the area where this elasticity gives a significant energy return.

Even with a "big basket" racket weighing less than 340 g and a balance point located 31 cm from the end of the handle, it is possible to give almost as much speed to the ball as with a racket having a corded surface of 451 cm2, un-weight of 275 g and a balance point 33 cm from the end of the handle.

Many beginners, old players and players who only play tennis occasionally, appreciate many such rackets requiring little effort for a satisfactory result.

But other players, especially the best, consider that very large dimensions of the frame increase the aerodynamic resistance of the racket, and make its handling difficult, preventing the rapid movements, for example necessary to return the service.

On the other hand, the speed of play, when it comes mainly from the great elasticity of the stringing of a racket "with a large basket", does not allow sufficient precision and control. Finally, it is likely that precision is affected by the deformations and vibrations caused by an energetic strike. With a frame of approximately oval shape, even if it is made with the best materials, these deformations and vibrations depend more or less on its dimensions.

Anyway, if almost all the players appreciate the advantages of rackets whose surface exceeds 451 cm2, it is especially rackets whose corded surface is less than 590 cm2 which are now manufactured. The best players often even use rackets with a surface area of only 540 cm2.

With such rackets, when the Player's address allows him to strike the ball at a point very close to the point where, with roughly oval corded surfaces, the longest uprights and the longest traverses, it is possible to '' obtain at the same time a good return, a good restitution of energy and a good precision of Play.

However, not all Players are skilled enough to achieve this result.

Consider for example what happens to the most important shots in modern tennis: Service and return service.

Studies on the wear of the strings and experiments carried out with stroboscopic and electronic equipment have shown that: if the players manage to strike the ball fairly easily generally by points close to the axis of symmetry X of the frame, when 'it is in particular a question of returning the fastest services of increasingly large players', even the best players lack the time to modify their gesture and above all, which is preferable, to move quickly enough so avoid hitting the ball at points far from the middle of the X axis.

However, for these returns of service, the Players hardly have the time to execute a large movement and must especially count on a sufficient and especially regular performance of the string to obtain enough speed and precision in the trajectory of balls to pass flush with the net to annoy the servers rushing forward.

On the other hand, voluntarily or instinctively, some players when they serve, also strike the ball by a point closer to the head of the racket than the spacer.

Unfortunately, with the usual oval shapes of the corded surface, the performance is modified as soon as the impact is far from the middle of the X axis because the length of the crossbeams decreases rapidly while on one side of the point of impact, the portion of the uprights between this point of impact and the frame also decreases.

With rackets of a more or less square shape, it is also possible to increase the general elasticity of the strung surface, but with significant drawbacks concerning the equality of tension of the strings after stringing and as with very large strung surfaces, with less precision in the game, an increase in vibrations and deformations of the frame and stresses creating possibilities of rupture at certain points.

It should also be noted that if, at the center of the rope, the useful elasticity of the crosspieces plays from the outside of the frame because the axes of the holes are practically in the extension of the crosspieces, on the contrary, with the frames approximately oval, the axes of the holes through which the crosspieces move closer to the head of the racket or the spacer, are inclined relative to the direction of the crosspieces, which means that the useful elasticity of said crosspieces only acts on reduced lengths between the holes of the holes on the inner side of the frame.

OBJECT OF THE INVENTION
The object of the present invention is a racket whose surface of the corded surface is preferably between 540 and 590 cm2, the center of percussion P (the point where the strike determines the least impact for the hand of the
Player, a simple rotation of the whole racket in the hand without translational effect and with the minimum of vibration), is close to the middle M of the Y axis, with which can be obtained an excellent performance and a high precision of
Game when the ball is struck near these points P and M and with which this output and this precision remain almost uniform over a much greater length than with an approximately oval corded surface, the. along and around the axis of symmetry X, while the results obtained, when the ball is struck by points relatively close to the head of the racket or the spacer, are comparable to those obtained with total surface areas strung much larger.

General description
The strung surface of the racket according to the invention comprises five zones separated by lines parallel to the axis Y, including a central zone A, in which there are at least three transverses, and also, both the center of percussion and the meeting point of the X and Y axes and, on either side of the central zone, two zones B and C also comprising at least each three beams whose average length, and consequently the elasticity, are greater that of the traverses of the central zone, and extending to the head of the racket or of the spacer, two other zones D and E, the surfaces of which are greater than those of the rackets whose corded surface is approximately oval.

The main characteristics of a nonlimiting example of the invention appear during a comparison between a strung surface according to the invention and the strung surfaces of two rackets widely used today.

- Figure 1 shows the strung surface of a racket,
the corded surface of 604 cm2 exceeds by 34% the surface
classic old 451 cm2, which puts it in the
category "super medium basket" - Figure 2 represents the corded area of the second of
these rackets whose corded surface of 533 cm2 exceeds
less than -20% that of 451 cm2, which puts it in the
category "small medium basket" - figure'3 represents the strung surface of a racket
according to the invention - Figure 4 shows' on a larger scale the surface
roped in Figure 3, the uprights not being shown
for the sake of simplicity.

In Figure 1, the longest uprights are 32 cm long and the longest cross members are 24 cm long.

In Figure 2, the longest uprights are 30.5 cm long and the longest cross members are 22.2 cm long.

In Figures 3 and 4, the longest uprights have the same length as those in Figure 2.

In FIG. 4, the dotted line represents the corded surface of FIG. 2.

Point M represents the point of intersection of the X and Y axes, and point P represents the center of percussion of the racket whose strung surface conforms to the invention.

Two dotted lines on the two sides of points M and P, between which striking the ball gives the best possible result, delimit a central surface A in which there are three cross beams. Two other lines delimit two zones B and C, in which four crosses are found on both sides of zone A, and also delimit two other 'zones D and E, extending respectively to the head of the racket and Up to to the spacer.

It can be seen in FIG. 4 that the three crosspieces located in zone A are approximately the same length as the central crosspieces of the surface of FIG. 2 represented by the dotted line in FIG. 4.

According to the invention, at least three of the crosspieces in zones B and C have lengths slightly greater is respectively from 5 to 10 mm than those of the crosspieces of zone A, and clearly greater than the lengths limited by the dotted line showing the zone roped in figure 2.

It can also be seen in FIG. 4 that the lengths of the cross beams of zones B and C automatically lead to an increase in the lengths of the first cross beams of zones D and E which are then much greater than they would be if they were limited by the dotted as parts of Figure 2.

Two lines in FIG. 1 limit two zones F and G whose widths parallel to the axis Y are found. equal to those of zones D and E.

In FIG. 4, it can be seen that the areas of zones D and E are much larger than if they were limited by the dotted line representing the corded area of FIG. 2.

On the other hand, by measuring the surfaces of zones D and E, and F and G, it can be seen that, although the total strung surface of the racket according to the invention is less than that of FIG. 1 (572 cm2 against - 604 cm2), the areas of zones D and E (136 cm2 and 135 cm2) are equal to or greater than those of zones F and G (135 cm2 and 131 cm2).

Benefits
Under these conditions, it is not astonishing that long tests in Play with rackets in accordance with the invention have demonstrated that the best players easily obtain great precision of play, even by not striking the ball exactly between the center of percussion and the geometric center while for all the players, the results are much better, than with approximately oval strung surfaces, when the ball is struck more or less far from points M and P in zones B and C .

As far as services are concerned, high speeds can be obtained by hitting the ball, for example in the middle of the line separating zones B and D and beyond closer to the head.

Experiments concerning energy restitution have been made. The yields on different parts of the rope were measured, on the one hand for three rackets comprising a corded surface in accordance with the invention, and on the other hand for three different conventional rackets, comprising approximately oval corded surfaces of 563 cm 2, 604 cm2 and 655 cm2.

The yield was measured by stroboscopy, at the head, in the center t at the bottom of each sieve.

Two experimental approaches were chosen.

- fixed racket, ball thrown by a mechanical launcher.

Efficiency is the ratio of the arrival speeds of the
ball on the sieve and back after hitting the sieve.

- in service situation with a player ranked 2-6.

For each of the two approaches, the analysis relates to 72 racket tests (24 at the head, 24 in the center, 24 at the bottom 1/4).

The functions "V in / V out" and "V racket / V ball" have been adjusted to lines valid for the experimental values. These functions are asymptotic for values below the minima and above the maxima.

The relatively average racket and ball speeds of the tester are due to the priority search for impact precision at one of the three points of the sieve.

In order to compare the different rackets, the yields are expressed as a percentage of the maximum yield point of each racket.

MEDIUM GAPS ON FIXED RACKET WITH MECHANICAL LAUNCHER
Example Racket A 100% - 50% = 50% Total difference = 59 X ioo - 91% = 9% Average difference = 29.5%
Results
A = 29.5%
B = 24.5%
C = 22% Average deviation "prototypes" (A, B, D) = 26.3% D '= 25%
E = 30%
F = 32% "Classic" average deviation (E, F, G) = 30%
G = 28%
Gross gain: 30 - 26.3 = 3.7%
Percentage gain: (3.7 I 30) x 100 = 12.3%
Statistical tests on significant averages.

AVERAGE GAP ON RACKET HELD BY A PLAYER
A = 100 - 95 = 5% Total difference = 13%
100 - 92 = 8% Average = 6.5%
A = 6.5%
B = 4% Average difference "prototypes" (A, B, D) = 4.3%
C = 13.5%
D = 2.5%
E = 2.5 X
F = 8.5% Average deviation * 'classic "(E, F, G) = 5.5%
G = 5.5
Gross gain: 5.5 - 4.3 = 1.2%
Percentage gain: (1.2 t 5.5) x 100 = 22 X.

On fixed racket
The prototypes have an average yield gap of 26.3%. For classic snowshoes this difference is 30%. The gross gain of 3.7% therefore reflects a net gain of 12.3%.

On racket held by a player
The average deviation for an average ball speed of 120 km / h is
4.2% for prototypes
5.5% for the classics.

The gross gain of 1.2% reflects a net gain of 22%.

Since Student's statistical test on means is significant, these gains cannot therefore be due to chance.

The hypothesis of a gain in homogeneity of yield underlying the design of these innovative sieves is verified by these results.

Other advantages
With an approximately oval corded surface, of very large dimension, one certainly obtains a high elasticity and also a relatively uniform yield over a large extent, but with the drawbacks mentioned above concerning the handling of the racket and its aerodynamic resistance, the precision of the Backlash, frame distortions, and vibrations.

With the rackets of reasonable dimensions in accordance with the invention, we return the services better, we can strike them with more force and in general, we obtain the advantages of roughly oval strung surfaces much larger and as regards the precision of play, the deformations of frame and its vibrations, the advantages corresponding to small corded surfaces like that represented by figure 2.

Indeed, the shape of the corded surface according to the invention implies for the two sides of the frame, in the vicinity of the two ends of the Y axis, sinuosities which have an effect comparable to that obtained by the depressions and reliefs that we observe on the sheets of the sides of motor cars.

These sinuosities stiffen the frame, reduce the risk of its deformation, and reduce the amount and duration of the vibrations caused by the striking of the ball, like a smaller frame.

The radii of curvature of the two sinuosities are moreover large enough so that the three cross beams of zone A have roughly the same length, while in zones B and C the holes through which the three cross beams closest to zone A can be drilled practically in the extension of the strings, which allows the elasticity of these to play from the outside of the frame unlike what happens with an approximately oval frame.

Uniformity of elasticity for the strung surface is often sought by differences in spacing between the strings, but with too large deviations, the precision is reduced by increasing the vibrations of the string.

On the other hand, we see in Figure 4 that the widths of the frame involved by the shape of the corded surface at the ends of the dotted lines separating lines B and D and C and E, were a very useful increase of the moment of inertia around the X axis of the racket compared to that of a racket with a corded surface and a frame of approximately oval shapes.

It goes without saying that many variants can be introduced, in particular by substitution of technically equivalent means without departing from the scope of the invention.

Claims (4)

1. Tennis racket constituted by a frame delimiting a  corded surface, a handle joined to the frame by a part  with a gap between the ends of the frame  then joining together to form the handle, a spacer  closing the frame, the corded surface consisting of  uprights parallel to the axis of symmetry X of the frame and  transverse parallel to a Y axis perpendicular to the X axis and  passing in the vicinity of the middle of the X axis, characterized by  that the corded surface has five zones including one zone  central A in which both the point of  meets the X and Y axes and the percussion center, and at  minus three traverses and two zones B and C, on the side and  other from the central area, in which are located  minus three beams whose average length exceeds that  of area A. 2. Racket according to claim 1, characterized in that  than the average length of three across each of the  zones B and C exceeds the average length of all  across zone A from 4 to 12 mm. 3. Racket according to claim 1, characterized in that  that the frame delimiting the corded surface includes,  and at the other ends of the Y axis, sinuosities including  the central part has a curvature whose center is  outside the frame and is therefore inverted compared to  the general curvature of the frame. 4. Racket according to claim 3, characterized in that  that the radii of curvature of the sinuosities are quite large  to give roughly the same length across the  zone A and give the holes through which pass at least  three across zones B and C, one direction  found roughly in the continuation of the cross.